POWER

The total energy given out by a source, as distinct from its INTENSITY which is the energy crossing a unit area in a unit time. Power is the rate of doing work and is measured in watts. An example of work done by sound is the moving a microphone DIAPHRAGM or the TYMPANIC MEMBRANE of the ear. However, the ear is sensitive to the rate of energy it receives, and interprets it as LOUDNESS.

Sound, however, contains little absolute power; a voice speaking softly may produce as little as 10-12 watts of power. A trombone playing fortissimo produces about 6.4 watts. The energy of a 40-watt bulb falling on an area of 1 cm2 at a distance of 1 cm produces the same energy per second as 1500 bass voices singing fortissimo.

Power level is measured in DECIBELs. See table below and Appendix D.

 Power ratio Decibels Current or voltage ratio Decibels 1 0 1 0 2 3.0 2 6.0 3 4.8 3 9.5 4 6.0 4 12.0 5 7.0 5 14.0 6 7.8 6 15.6 7 8.5 7 16.9 8 9.0 8 18.1 9 9.5 9 19.1 10 10 10 20 100 20 100 40 1,000 30 1,000 60 10,000 40 10,000 80 100,000 50 100,000 100 1,000,000 60 1,000,000 120

Table for conversion of power ratios to decibels.

In an electrical circuit, power equals the voltage times the current, as established by Ohm's Law. See also: ROOT MEAN SQUARE.

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